Photochromic Mechanism and Dual-Phase Formation in Oxygen-Containing Rare-Earth Hydride Thin Films

摘要

The phase formation of a photochromic Gd-0.31(H0.55O0.45)(0.69)thin film, grown by reactive magnetron sputtering, is critically evaluated. Oxygen is preferably incorporated into the underdense columnar grain boundaries, when the as-deposited gadolinium hydride film is exposed to ambient conditions. Two phases, Gd(2)O(3)and GdH2, are formed with significant compressive residual stress of 5.9 +/- 1.5 GPa. These findings, extracted from transmission electron microscopy, X-ray diffraction and atom probe tomography, provide a straightforward explanation for the photochromic effect. The mechanism can be understood as photon-induced hydrogen transfer between the two phases, identical in nature to the photochromic effect in bulk yttrium hydride at high pressure.